1. Field of the Invention
The present invention relates to a semiconductor device.
2. Related Art
A degree of integration of a ferroelectric memory having a ferroelectric capacitor is increasingly advanced. Accordingly, the size of the ferroelectric capacitor is decreased from several microns to submicrons. When the ferroelectric capacitor is micropatterned, an amount of residual polarization of the ferroelectric capacitor decreases. The micropatterned ferroelectric capacitor is easily damaged in hard mask formation in CVD (Chemical Vapor Deposition), processing of the capacitor in the RIE (Reactive Ion Etching), formation of an insulating interlayer in CVD, or the like in steps of manufacturing the capacitor. By the process damage, an amount of residual polarization of the ferroelectric capacitor also decreases. The decrease in amount of residual polarization is caused by fixed charges such as hydrogen trap or oxygen deficit occurring in a ferroelectric film of the ferroelectric capacitor or on an interface between an electrode and the ferroelectric film. Characteristic deterioration such as a decrease in amount of residual polarization degrades the reliability of the ferroelectric memory.
When the ferroelectric capacitor has a size of a sub-micron level, an amount of polarization of the ferroelectric capacitor becomes unstable because of an influence from a peripheral portion of the ferroelectric capacitor. In particular, when the ferroelectric capacitor is operated with a low voltage, the ferroelectric film must be thin. When the thin ferroelectric film is to be used, it is important to thermally or temporally stabilize the amount of polarization of the ferroelectric capacitor.